In this paper I propose to consider a certain set of notions in Kant as subsumable under a single notion – that of the soul’s intensity – as well as the possibility of a transcendental grounding of this notion within Kant’s critical framework. First, I discuss what it means for Kant to attribute intensive magnitude to the soul, starting with his response to Mendelssohn where Kant introduces the soul’s intensity as a metaphysical notion immanent to the principles of rational psychology. I show, however, that in Kant’s counter-argument there occurs a subtle though crucial shift in perspective – from the soul’s substance to its powers. Then I move on to consider three fundamental variants upon the soul’s intensity – intensities of representation, of life, and of cognition – each governed, I argue, by the implied notions of measure of intensity and its balance. Also, I examine Kant’s accounts of the life of a species and the necessity of sickness; of intensity of “enlightenment” in a society and the benefit of ignorance; and of sermon as a practical exertion of cognition’s intensity. Next, the aforementioned shift of emphasis allows me to demonstrate that the notion of the soul’s intensity can indeed be transcendentally justified by appealing to Kant’s principle of the Anticipations of Perception. Finally, I conclude with an appendix on the possible connection of the soul’s intensity to Kant’s aesthetics.